224 



PHYSIOLOGY 



CHAP. 



to the roots of a plant which- spread and multiply in suitable 

 nutritious soil, the soil being represented by the. hypertrophic 

 placental decidua. These much ramified and vascularised villi do 

 not emerge uniformly from the placental chorion, but appear in 

 clump-like groups or tufts called cotyledons. On the other hand, 

 through proliferation of the decidual tissue, more or less developed 



FIG. 89. Terminal portion of trunk of villi of a placenta at term : injection of the arteries 

 (red) ; of the veins (blue). (After Bumm.) 



ta, defining as many small spaces, are found between the 

 cotyledons. 



It is thought by many that a solid adhesion of the surface of 

 the villi to that of the decidua occurs only in the trunk and main 

 branches of the villi (roots of attachment), the larger number of 

 the ramifications of the villi terminating freely in a system of 

 intervillous spaces found between the chorion and the decidua 

 (free prolongations of the villi). In a few weeks the maternal 

 blood penetrates into this system of intervillous spaces as a 



